In the field of offshore structures or in the field of line pipes, there is an ongoing trend of advancing development of energy resources in very deep waters, expanding resource exploration/mining zone to an extreme sea area such as Arctic sea, and growing in the equipment size. Against this background of technical trend, the offshore structure or line pipe design is progressing to achieve high strength and high toughness, and more stringent requirements are imposed on the performance of the weld joint.
On the other hand, as for the welding material, a flux-cored wire for all-position welding is demanded in view of higher efficiency. In addition, high fracture toughness is also required for the weld metal obtained.
However, a conventional flux-cored wire for all-position welding forms a weld metal having a high oxygen amount and therefore, when gas-shielded arc welding is performed using the wire, it is difficult to ensure low-temperature toughness of the weld joint part.
Accordingly, for example, Patent Document 1 discloses a technique of restricting the steel outer sheath components and adding Cu, Ni, Ti and B to the flux filled, thereby greatly enhancing the seawater corrosion resistance of weld metal and obtaining low-temperature toughness.